I remember learning to sew and thinking that zippers were so Daunting, I was very concerned about putting one in and tried to avoid it like the plague. But eventually, I put one in, and you know what? It's pretty easy!
Start by pinning the zipper onto your fabric, right sides together. Like this:
Using your zipper foot, sew down with a straight stitch very close to the actual zipper.
Fold the zipper under, and top stitch into place. I stitch about a 1/4 away from the fabric edge.
Stitching the other side down can get tricky, but with some maneuvering isn't too bad. I opened the zipper here, but you could leave it closed. Again, stitch close to the zipper.
Turn the zipper out, top stitch again, and you're done. Now open and close the zipper a few times and congratulate yourself!